According to a known seat for a vehicle, a seatback portion of a backseat is tilted (retractable type), and/or is detachable from a vehicle floor (detachable type), so as to reduce a surface level difference on the vehicle floor inside the vehicle, thus enabling an effective use of a space inside the vehicle. Such retractable type seat may be fixed at a side surface of the vehicle compartment, and such detachable type seat may be fixed at the vehicle floor, for example, through a lock apparatus. As an example of such seat apparatus, JP2006-248330A (hereinafter, referred to as reference 1) discloses a seat lock assembly (lock apparatus), which is provided at a side surface of a vehicle compartment and at a side surface of a seatback for fixing (locking) the seatback to the side surface of the vehicle compartment. The seat lock assembly includes a striker, a base plate (first plate), a back plate (second plate), a latch (hook member) and a ratchet (pawl member).
According to the reference 1, the striker is fixedly connected to the side surface of the vehicle compartment. The base plate and the back plate are arranged to overlap each other and are connected to the side surface of the seatback so that the base plate faces the side surface of the seatback. Further, the base plate and the back plate include striker grooves, respectively, into which the striker is inserted. A hook member is pivotably provided between the base plate and the back plate and is biased in a lock release direction by a spring. The hook member includes an engagement groove, with which the striker inserted into the striker grooves of the base plate and the back plate is engaged. A pawl member is pivotably provided between the base plate and the back plate so as to suppress a pivotal movement of the hook member in a lock direction.
Due to such lock apparatus, when the striker is interposed by inner end walls of the striker grooves of the base plate and the back plate and side surfaces of the engagement groove formed at the hook member, the seatback is locked to the side surface of the vehicle compartment (hereinafter, such condition is referred to as a locked state). When an external force is applied to the striker in a direction to release the striker from the striker grooves of the base plate and the back plate in the locked state, the pawl member makes contact with the hook member to suppress a pivotal movement of the hook member for preventing the hook member from pivoting by a biasing force of the spring to be in a lock released state.
The striker groove is formed at each of the base plate and the back plate so as to extend from a central portion of a side surface of the corresponding plates. Further, attachment holes (attachment portions) are formed at both sides of each striker groove so that the base plate and the back plate are attached to the side surface of the seatback. Accordingly, when the external force is applied to the striker in a direction to release the striker from the striker grooves, a reacting force is generated at the attachment holes (attachment portions) provided at each of the base plate and the back plate, and the base plate and the back plate are forced to strain in a direction where an opening portion of the groove portion expands. Further, a bent portion may be formed at the base plate for housing the latch and the ratchet. In such a condition, the rigidity of the base plate is reduced to be lower than the rigidity of the back plate. Accordingly, when the base plate includes a shape-changing portion from which a cross sectional shape and/or a cross sectional area of the base plate changes, the reacting force is intensively generated at the shape-changing portion, and the base plate may accordingly be deformed and/or damaged.
A need thus exists for a lock apparatus of a seat for a vehicle, which is not susceptible to the drawback mentioned above.